1. Field of the Invention
This invention relates generally to insulators for igniters of internal combustion engines, such as insulators for corona igniters or spark plugs, and methods of forming the insulators.
2. Related Art
Ignition devices for use in internal combustion engine applications, such as corona igniters and spark plugs, include an insulator surrounding a central electrode. The insulator is typically formed of ceramic material, such as alumina, which is able to withstand high temperatures encountered in a combustion chamber of the internal combustion engine. However, the performance of the ignition device can be restricted by the ceramic insulator. For example, in corona igniters, when the insulator is formed of alumina ceramic having a relative permittivity of about 10 to 10.5, the electrical efficiency is limited due to electrical losses. These electrical losses are caused by charge stored in the alumina ceramic, which is typically at a capacitance of about 15 picofarads. The electrical efficiency of the corona igniter could be increased by about 50% if the insulator were formed of a material having a relative permittivity of about 5, such as polytetrafluoroethylene (PTFE). However, PTFE is not able to withstand the high temperatures of the internal combustion engine, and thus ceramic materials are still preferred.